The present invention relates to a digital camera which employs an image pick-up device such as a CCD (charge-coupled device).
Recently, digital cameras which record image data on a medium such as a flash memory card, a smart card or the like have become widespread. A basic configuration of a digital camera is similar to a camera which uses a silver-salt film. That is, the digital camera includes components such as a photographing optical system for forming an image of an object on an image plane, and an aperture mechanism. In the digital camera, a CCD is provided instead of the photographing film on the Image plane.
FIG. 1 is a cross sectional view of a CCD 3 which is generally employed in a conventional digital camera. As shown in FIG. 1, on an upper portion of the CCD 3, a plurality of photoreceptors (photo diodes) 32 and transistors for transferring charges (not shown) are formed.
Above the photodiodes 32, apertures 33a are formed, respectively. The apertures 33a are covered with a plurality of micro-lenses 34, respectively, which form an image on the photodiodes 32 (i.e., on a light-receptive surface of the CCD 3).
Since the micro-lenses 34 converge light on the light-receptive surface of the CCD 3, the photographing optical system is required to form an image on the rear side of the light-receptive surface of the CCD 3. For this purpose, the photographing optical system should be configured such that rays of light incident on the micro-lens 34 are substantially parallel. That is, the photographing optical system in the digital camera is required to be substantially telecentric.
In a camera utilizing the silver-salt film, by making use of depth of fields, it is possible to intentionally form a defocused (i.e., out-of-focus) portion In an image of the object For example, by fully opening the aperture, a central object is focused, while a background is defocused. In the case of the digital camera, since the photographing optical system has the telecentricity as described above, it is difficult to obtain an image whose background is sufficiently defocused. That is, because of the telecentricity, the depth-of-fields of the digital camera is deeper than that of the camera which uses the silver-salt film.
Therefore, in order to obtain an image whose background is appropriately defocused, the image data should be once transmitted to a computer and is retouched using a photo retouching software.